One of the problems encountered in using pneumatic tools is maintaining an adequate air supply to the motor. Low supply pressure can be caused by several things: restricted hoses, leaky couplings, extra long hoses, or excess demand on the system. When the supply pressure is too low, pneumatic tools may malfunction causing damage to the tool or to the workpiece, or the tools may perform inadequately. For example, a pneumatic screwdriver or nutrunner may not maintain the required torque in tightening if the supply air pressure is too low. Also, some pneumatic tools have air operated clutches, gear shifts, control valves, depth sensing retract controls and other air pressure operated components requiring air pressure to be controlled within a suitable range and above a certain minimum pressure to insure proper function. It would be better for the tools to be shut down completely when the supply pressure is too low than to operate at less than a desired supply level. Pneumatic tools need the safeguard of some device to shut off the air supply when the pressure becomes too low thereby shutting down the pneumatic tool.
In the past, one method of providing this safeguard was to use a cut-off valve at a control panel remote from the air motor. Since this control was remote, it would not sense the pressure of the air supply actually reaching the tool. Also, a remote device may not be utilized by the operator as desired by the tool manufacturer. Therefore, a need existed for a built-in device that would shut off the air supply when the pressure was insufficient.
In addition, it would also be beneficial if the air flowing through a built-in pressure sensing device would be supplied to the air operated components, e.g. clutches, gear shifts, etc., through a single air line or manifold. Thus, the air control system would be at a uniform pressure throughout and this pressure would be simultaneously present at the pressure sensing device. This is desireable since the pressure sensing device would be monitoring the actual pressure supplied to the air operated components. Also if the pressure should drop within the air control system due to a low supply pressure, intentional venting by a "motor stop" signal valve, intentional venting by a built-in or remote "stop button", excessive leakage, or for any other reason, the pressure sensing device would shut off the air supply to the motor and to the air control system.